JP5105038B2 - Method for producing powder permanent magnet material and powder permanent magnet material - Google Patents

Description

  The present invention provides materials based on cobalt and zinc that are useful as new permanent magnet materials.

Rare earth magnets such as samarium / cobalt magnets and neodymium / iron / boron magnets are widely used as high-performance magnets from computer peripherals, consumer electronics, measurement and communication equipment to automobiles and medical equipment. Increasing year by year. Ferrite magnets are inferior in magnetic properties to high-performance neodymium / iron / boron magnets, but they are oxide magnets and are cheaper and chemically stable. It is a magnet that is widely used in large quantities. Alnico magnets are used in measuring instruments because of their excellent temperature characteristics. The above rare earth magnets and ferrite magnets are used not only as solid magnets (sintered magnets) but also as bonded magnets (plastic magnets) in which magnet powder is bonded with epoxy resin, etc., for refrigerator packings and motors, Due to the features such as light weight and lack of cracks, the proportion of the bonded magnet used in the entire magnet is increasing year by year.
As a method for producing a permanent magnet powder, there is generally a physical method of mechanically pulverizing a metal or ceramic lump (bulk). Further, in some rare earth magnets, a ribbon (ribbon) is produced by a rapid solidification method and then pulverized (see, for example, Patent Document 1). However, it is difficult to produce powders having uniform shapes and particle sizes by these mechanical pulverization methods, and it is particularly difficult to produce spherical fine powders.
In addition, it is possible to produce a spherical powder by a gas atomizing method or the like (see, for example, Patent Document 2). Not suitable for.
JP-A-10-317110 Japanese Patent Laid-Open No. 2005-064096

The inventor has found that there are the following problems with permanent magnet materials such as rare earth magnets and ferrite magnets that are currently widely used.
High-performance samarium / cobalt magnets and neodymium / iron / boron magnets such as samarium and iron / boron magnets, whose production volumes are currently increasing, are expensive and have high corrosion resistance because they are mainly composed of rare earth metals such as samarium and neodymium. bad. Further, since the ferrite magnet is made of an oxide, the corrosion resistance is good, but since it is an oxide, there is a drawback that the amount of transition metal is small and therefore the saturation magnetization is small.
In the present invention, a powder magnet material having a composition different from that of a conventional permanent magnet material and having a uniform shape and particle size is produced by a method different from the conventional method. That is, the present invention produces a new powdered magnet material based on cobalt and zinc.

As a result of intensive studies on the permanent magnetization of a new alloy containing no rare earth metal, the inventor has found that cobalt powder can be produced by a chemical reduction method. Furthermore, it has been found that the coercive force essential as a permanent magnet is generated by adding zinc and simultaneously performing chemical reduction.
These alloy powders are metals, have high saturation magnetization, and exhibit magnetic properties that can be used as permanent magnets as they are. Moreover, the cobalt zinc alloy powder produced by the chemical reduction method can be used as a bonded magnet by bonding with a resin or the like.

  The permanent magnet material of the present invention is a cobalt zinc alloy powder produced by a chemical reduction method, has a uniform shape and particle size, has a large degree of freedom in shape, and can be obtained at a relatively low cost.

  The best mode for carrying out the present invention will be described below.

  First, as an example of the production of cobalt zinc alloy powder by the chemical reduction method, a case where cobalt chloride hexahydrate and zinc sulfate heptahydrate are used as raw materials and sodium hypophosphite as a phosphinate is used as a reducing agent is shown. . A sample was prepared by adding sodium hypophosphite while stirring a solution of trisodium citrate dihydrate as a complexing agent in cobalt chloride hexahydrate. The pH of the solution was adjusted with boric acid and sodium hydroxide. The temperature of the solution was heated to 90 ° C.

  The appearance of the obtained sample was examined with a scanning electron microscope (SEM). The results are shown in FIG. It was found that the particle diameter of the cobalt zinc alloy powder produced by the chemical reduction method did not change greatly even when the pH concentration was changed, and was about 1 μm, and the shape was spherical. Cobalt is a magnetic material, but zinc is non-magnetic, so a cobalt-zinc alloy containing a large amount of zinc does not exhibit high magnetization. Therefore, the zinc content of the cobalt zinc alloy powder was changed within a range of 25% or less, and it was found that a spherical powder could be obtained regardless of the zinc content. The magnetic characteristics mainly depend on the cobalt content, and it was found that the saturation magnetization decreases with increasing zinc content. As a range in which practical magnetic properties can be obtained, the zinc content of the cobalt zinc alloy powder is set to 25% or less.

  Next, FIG. 2 shows a magnetic hysteresis curve of a sample of cobalt zinc alloy powder (zinc content 4 wt%) produced by the chemical reduction method. The horizontal axis represents the magnetic field applied to the alloy, and the vertical axis represents the magnetization generated in the alloy. The saturation magnetization is the maximum magnetization value, and the coercive force is the magnetic field when the magnetization becomes zero, that is, the value at the intersection of the hysteresis curve and the horizontal axis. As shown in Fig. 2, the cobalt-zinc alloy powder produced by chemical reduction has a large saturation magnetization of 125 emu / g and is a promising magnetic material. The coercive force important as a permanent magnet is 1.6 kOe, which is higher than that of alnico magnets. Also showed a high coercivity.

  When the composition of the cobalt zinc alloy powder produced by the chemical reduction method was analyzed, it was found that this sample contained 5-8 wt% phosphorus. This is because sodium hypophosphite was used as the reducing agent. The powder produced by the chemical reduction method generally contains several percent of phosphorus or boron depending on the reducing agent used.

  Next, as an example of production of cobalt zinc alloy powder by the chemical reduction method, a case where cobalt sulfate heptahydrate and zinc sulfate heptahydrate are used as raw materials and sodium hypophosphite is used as a reducing agent is shown. A sample was prepared by adding sodium hypophosphite while stirring a solution of trisodium citrate dihydrate as a complexing agent in cobalt sulfate heptahydrate. The pH of the solution was adjusted with boric acid and sodium hydroxide. The temperature of the solution was heated to 90 ° C.

  The obtained cobalt zinc alloy powder has a particle size and magnetic properties that can be obtained in the same manner as when cobalt chloride hexahydrate is used as a raw material, and that the magnetic properties of the obtained cobalt zinc alloy powder. Was found to have a high coercivity.

  Since it was found that phosphinates can be obtained by a chemical reduction method in a spherical shape and having a coercive force regardless of the raw materials, an example of chemical reduction using tetrahydroborate will be described below. Here, a case where cobalt sulfate heptahydrate and zinc sulfate heptahydrate are used as raw materials and sodium borohydride is used as a reducing agent as a tetrahydroborate is shown. The chemical reduction was performed by adding sodium borohydride as a reducing agent while stirring a solution of zinc sulfate heptahydrate added to zinc sulfate heptahydrate to prepare a sample. The pH of the reaction solution was adjusted with hydrochloric acid and sodium hydroxide. The temperature of the reaction solution was room temperature.

  The appearance of the obtained sample was examined with a scanning electron microscope (SEM). The result is shown in FIG. For comparison, a photograph taken at the same magnification as in FIG. 1 is shown. The particle size of cobalt zinc alloy powder prepared by chemical reduction method using tetrahydroborate is much finer than that using phosphinate, and its particle size is about 0.1μm from the enlarged photograph. I understood it.

  However, the saturation magnetization of cobalt zinc alloy powder prepared by chemical reduction using tetrahydroborate is as large as 120 emu / g, and the coercive force important as a permanent magnet is 1.5 kOe, which is almost the same as when phosphinate is used. It turns out that it is the same.

  The composition of cobalt zinc alloy powder prepared by chemical reduction was analyzed, and it was found that this sample contained 5-8 wt% boron. This is because tetrahydroborate was used as the reducing agent. Thus, it was found that the powder produced by the chemical reduction method contained several percent of phosphorus, boron and the like depending on the reducing agent used.

  The permanent magnet material of the present invention can be widely used from computer peripheral devices, consumer electronic devices, measuring / communication devices to automobiles and medical devices.

It is an external appearance photograph by the scanning electron microscope of the cobalt zinc alloy powder produced by the chemical reduction method using the phosphinate as a reducing agent. It is a hysteresis curve of the cobalt zinc alloy powder produced by the chemical reduction method. It is an external appearance photograph by the scanning electron microscope of the cobalt zinc alloy powder produced by the chemical reduction method using tetrahydroborate as a reducing agent.

Claims (5)

  By mixing a reducing agent aqueous solution with a mixed solution of cobalt salt aqueous solution and zinc salt aqueous solution and simultaneously reducing cobalt ions and zinc ions, the cobalt zinc alloy powder having a spherical shape and an average particle size of 0.1-2.0 μm can be obtained. A method for producing a powder permanent magnet material, comprising:   The method for producing a powder permanent magnet material according to claim 1, wherein the reducing agent contained in the reducing agent aqueous solution is a phosphinate.   The method for producing a powder permanent magnet material according to claim 1, wherein the reducing agent contained in the reducing agent aqueous solution is tetrahydroborate. A powdered permanent magnet material produced by the method according to any one of claims 1 to 3, the shape is spherical, powdered permanent magnet material, wherein the average particle size of 0.1-2.0Myuemu. The powder permanent magnet material according to claim 4, wherein the composition is expressed by Co _1-m Zn _m X (where X is P or B coming from a reducing agent, and the composition ratio is 0 < m ≦ 25 atomic%. ).